Maintaining a constant power factor in a system of distribution.



A. A. TIRRILL.

MAINTAINING A CONSTANT POWER FACTOR IN A SYSTEM OF DISTRIBUTION.

APPLICATION FILED AUG. 20, 1908.

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ALLEN A. TIRRILL, OF SC HENECTADY, NEW YORK, ASSIGNOB T GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

MAINTAINING A GONSTANT POWER FACTOR IN A SYSTEM OF DISTRIBUTION.

Specification of Letters Patent.

Patented Jan. 20,1914.

Application filed August 20, 1908. Serial No. 449,402.

' bution, of which the followmg is a specification.

This invention relates to alternating current systems of distrlbution inwhich the phase relation between the current and potential is regulatedby a synchronous motor or the like. .The invention has especialreference to means for automatically regulating the field magnetizationof such synchronous machine. It is well known that by varying the fieldexcitation of a synchronous motor connected to an alternating currentdistributing system the power actor of the system can be maintainedconstant.

' The object of my invention is to provide an improved means forautomatically regulating the field excitation of the synchronous machinein response to a change in the power factor of the circuit, for thepurpose of maintaining the power factor constant.

In carrying out my invention I employ a modified Tirrill regulator forcontrolling the excitation of the field of the synchronous machine,which preferably floats on the system. type except that in place of theusual alternating current control magnet, I use a solenoid having twopotential windings, respectively supplied with current from twopotential transformers across two sides of the line, and a floatingcurrent coil mounted on the core of the solenoid and supplied withcurrent from a current transformer on the line conductor located betweenthe two transformers. To prevent too rapid movements of the movablecoil, a dash-pot is connected to the core. arrangement is to hasten orretard the tinn of the closing of the main control contacts inaccordance with the fluctuations in phase between the current andpotential so as to increase or decrease the field excitation of thesynchronous motor and thereby throw" The regulator is of the standard.

The effect of this The supply mains 1, 2, 3 of a three phase linefurnish current to a load circuit Land also to a synchronous motor 5whose field coil 6 is energized by an exciter 7. A rheostat 8 in serieswith the field coil 6 enables the magnetization of the synchronous motorheld to be adjusted. The circuit of the exciter field coil 9 alsocontains an adjustable resistor 10 which is shunted by the contacts 11,controlled by the differentially wound relay 12, taking current from theexciter bosses 13. The relay is controlled by a pair of floatingcontacts 14 carried on levers 15, 16, the former being attached to themovable core 17 of a direct current control magnet 18 which is connectedacross the mains of the exciter. The pull of the magnet is opposed by aspring 19. The other lever 16 is attached to cores 20 which are attachedto a stem 20 and move freely up and down through fixed coils 21. Thestem 20 carries a floating coil 22. A dash-pot 23 is connected with saidcore to retard its movements The coil 22 is in circuit with a currenttransformer 24.- on one of the line conductors. Potential transformers25 are connected across the line, each being in series with one of thecoils 21. Non-inductive resistors 26 reduce the current in the coils 21.

The operation is as follows: Suppose that the synchronous motor isrunning without load, and the floating control contacts and other partsare adjusted so that the synchronous motor is excited to such a value asto give neither leading or lagging currents; in other words, let thepower factor of the system be unity. Under thesecondit-ions, the currentand potential being in phase with each other and 120 electricaldegreesapart in the respective mains, the resultant force exerted by the upperpotential coil 21 upon the current coil 22 is equal and opposite to theresultant force exerted by the lower potential coil 21 upon the currentcoil 22. This will be true irrespective of the amount of current flowingin the current coil, pron." or) greater. This unbalances the resultantforces and causes the coil 22 to move upward or downward according towhich Way the power factor tends to vary from unity. For example, if thecurrent tends to lag behind the electromoti've force the coil movesdown, thereby raising the contact 14 on the lever l6.and causing it toclose sooner and remain closed longer in the rapid opening and closingaction of the Tirrill regulator. This causes an overexcitation of thefield winding 6 of the synchronous motor, which takes a leading currentto counteract the lag in the system and restores the power factor tounity, providing the motor is of suiiicient capacity and the inherentregulation is suiiiciently close. For a leading current on the system, areverse action will take place.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is, 1. Ina polyphase system of distribution having a synchronousdynamo electric machine connected thereto for controlling the powerfactor of the system, means for controlling the excitation of saidsynchronous dynamo electric machine including the combination of aresistance, a shunt circuit around said resistance, a pair of floatingcontacts controlling said shunt circuit, means responsive to thepotential impressed on the field of said synchronous machine forcontrolling one of said floating contacts, and means responsive to thepower factor of the system for controlling the other of said floatingcontacts, said last named means ost-e74 comprising relatively movablecoils responsive respectively to the potential across a plurality of thesides of said system of distribution and to the current flowing in saidsystem.

2. In a three-phase system of distribution having a synchronous dynamoelectric machine connected thereto for controlling the power factor ofthe system, means for controlling the excitation of said synchronousdynamo electric machine including the combination of a resistance, ashunt circuit around said resistance, a pair of floating contactscontrolling said shunt circuit, means responsive to the potentialimpressed on the field of the-synchronous machine for controlling one ofthe said floating contacts, and means responsive to the power factor ofthe system for controlling the other of said floating contacts, saidlast named means comprising a pair of spaced fixed potential coilsconnected across two sides of the system, a movable current coil locatedbetween said potential coils and connected to receive current from theline conductor located between the two potential coils and meansconnecting said current coil to said last named floating contact.

in Witness whereof, I have hereunto set my hand this 18th day of August,1908.

ALLEN A. TIRRILL Witnesses: I

BENJAMIN B. li'lULL, HELEN @aroan

